The requirements for monitoring and controlling stack gas pollutants have resulted in the development of solid electrolyte gas sensors having compositions uniquely responsive to gaseous pollutants such as SO.sub.2. Solid electrolyte sensors for monitoring gases containing anhydrides or related compounds in air or in oxygen bearing gases have been described in detail in Canadian Patents No. 1,002,599 and 1,040,264, both of which have been assigned to the assignee of the present invention and are incorporated herein by reference. The above-referenced sensors are electrochemical cells which generate an EMF signal corresponding to the difference in partial pressure of the monitored gas constituent across the solid electrolyte sensor. Typically, the solid state sensor includes an ion conductive solid electrolyte and electrodes disposed on opposite surfaces thereof. The stack gas, or monitored gas environment, contacts a sensing electrode while the opposite electrode serves as a reference electrode. In order for the EMF signal to be a true indication of the SO.sub.2 partial pressure of the monitored gas environment, it is necessary to compensate for, or correct for, variations in the oxygen partial pressure in the monitored gas environment.
Typically, this correction, or compensation, is provided electronically through mathematical manipulation of the EMF output signal of an SO.sub.2 measuring solid electrolyte sensor and the EMF output signal of an oxygen measuring solid electrolyte sensor.